Microwave cavity product transport system

ABSTRACT

A microwave applicator is described for treating a product which is continuously passed through a multi-mode microwave cavity. The applicator includes a roller transport system for conveying the product through the cavity. Each of the product rollers of the transport system is made from a quartz tube having end plugs in its opposite ends. The rollers are positioned between a pair of spaced apart, generally parallel support rails, and spherical bearing balls extend inwardly from opposed locations on the rails into associated axial cavities in the end plugs of each roller to provide a bearing for rotation of such roller. A flexible drive belt is connected exterior of the cavity with a motor and passes through a wall of such cavity into frictional engagement with the peripheral surface of each of the rollers to rotatably drive the same.

United States Patent 11 1 Anderson et al.

[ Oct. 28, 1975 MICROWAVE CAVITY PRODUCT TRANSPORT SYSTEM of Calif.

[73] Assignee: Gerling Moore Inc., Palo Alto, Calif.

[22] Filed: May 28, 1974 [21] Appl. No.: 473,335

52 US. c1 219/1055 A; 198/127 R; 308/20 51 1m.c1. 1105B 5/00 58 Field of Search... 219/1055 A, 10.55 F, 10.69; 308/219, 233, DIG. 7, DIG. s, 20, 135, 143,

173, 184, 238; 198/127 R; 193/35 R, 37 R [56] References Cited UNITED STATES PATENTS 2,684,881 7/1954 Sparklin 308/233 Primary E.\'aminerBruce A. Reynolds Attorney, Agent, or FirmC. Michael Zimmerman, Esq.

[57] ABSTRACT A microwave applicator is described for treating a product which is continuously passed through a multimode microwave cavity. The applicator includes a roller transport system for conveying the product through the cavity. Each of the product rollers of the transport system is made from a quartz tube having end plugs in its opposite ends. The rollers are positioned between a pair of spaced apart, generally parallel support rails, and spherical bearing balls extend inwardly from opposed locations on the rails into associated axial cavities in the end plugs of each roller to provide a bearing for rotation of such roller. A flexible drive belt is connected exterior of the cavity with a motor and passes through a wall of such cavity into frictional engagement with the peripheral surface of each of the rollers to rotatably drive the same.

10 Claims, 4 Drawing Figures US. Patent Oct. 28, 1975 Sheet10f 2 3,916,136

U.S. Patent Oct. 28, 1975 Sheet2 0f2 MICROWAVE CAVITY PRODUCT TRANSPORT SYSTEM r BACKGROUND OF THE INVENTION This invention relates to an applicator for treating a product with electromagnetic energy and, more partic ularly, to such an applicator having a cavity resonator and a transport system for conveying product through such cavity which provides a minimum of interference with uniform treatment of the product.

Microwave radiation can provide thermal energy within the interior of a dielectric material without the necessity of such thermal energy being conveyed by conductioninwardly of the material from its surface. For this reason, microwave energy is being inceasingly used to heat or otherwise treat products which require uniform heating throughout their mass, without surface overheating. For example, microwave energy is now commonly used to vulcanize and foam natural and synthetic rubber products. For such treatment, it is the usual practice to continually pass product to be treated through a standing wave microwave cavity resonator which defines, in effect, a treatment Zone for the product.

Various product transport systems have been devised for supporting a product as it is passed through a microwave cavity. There are cetain criteria which must be satisfied by such a system. Insofar as treatment of rubber products are concerned, the primary criteria to date has been that the product bearing surface be capbable of maintaining its structural integrity when subjected to high temperatures. In this connection it is the usual practice to introduce rubber products to be treated into a microwave cavity immediately after such products have been formed by, for example, extrusion. The result is that the product itself is at a high temperature, e.g., about 225 F. Moreover, heated air at a temperature in the neighborhood of 200 F is often introduced into the cavity for moisture removal. Thus, the thermal conditions to which a product transport system is subject are often harsh.

Typically, transport systems designed for operation in such environments have included a plurality of metal conveyor rollers to define a support surface for the product along its path of travel through the cavity. It has been felt that the rollers must be made of a metal in order to withstand the high temperature environment. Metal rollers also have the advantages of being capable of being precisely sized and relatively easily mounted for rotation. However, it has been found that metal rollers affect the uniformity with which a product is heated. More particularly, it has been found that when products or parts made from rubber are passed through a microwave cavity on metal rollers, the per tions of the rubber immediately adjacent to the rollers become heated to a significantly greater degree than the remainder of the rubber. This is especially disadvantageous with respect to the foaming of certain rubber products because it can cause both surface burning and mishapen parts.

In addition to the above, arrangements provided in the past for rotatably driving the rollers to transport a product through the cavity have been far from ideal. They have, in general, been relatively complicated and most often required passsage of a driving axle for each roller through the wall of the cavity. This has resulted in radiaton leakage problems.

SUMMARY OF THE INVENTION The present invention relates to a product transport system for a microwave cavity applicator which alleviates the above problems. Such product transport system includes, as is usual, a plurality of rollers which are maintained in alignment by a mounting structure within the cavity to define a support surface for product to be passed through the cavity. As a particularly salient feature of the instant invention, the product bearing surface of each of the rollers is, however, of a dielectric material which is transparent to the electromagnetic radiation supported within the cavity. It has been found that when the product bearing surface of the rollers is of such a material, products conveyed tby the same through a cavity are not overheated adjacent where they engage the rollers. Such a dielectric material presents a minimum of disturbance to the electromagnetic energy field in the cavity adjacent the product passing therethrough. The dielectric material of the roller product bearing surface is also most desirably one capable of maintaining its structural integrity both when contacted by a heated product and when subjected to a high temperature environment within the cavity.

A material meeting the above criteria which has been found to be especially satisfactory is quartz. The invention further includes a mounting structure for maintaining the rollers in alignment which is especially adapted for use with such rollers. The mounting structure includes a pair of spaced apart, generally parallel support rails extending along the path of travel of the product and between which the rollers extend. Bearing projections extend inwardly of the support rails for rotatably mounting the rollers, each of which bearing projections extends axially into the adjacent end of a roller associated therewith. Most desirably, each of the bearing projections terminates in a spherical bearing ball which engages an inner cylindrical bearing surface of the roller end cavity. This provides, in effect, a universal joint for the bearing having a minimum of bearing surface contact and, hence, a minimum of bearing friction.

As another salient feature of the instant invention, the produce transport system includes a simple and yet effective and radiation leakage safe arrangement for axially rotating the rollers from the exterior of the cavity to convey product therethrough. Such an arrangement includes a source of motive power, such as an electric motor, positioned exteriorly of the cavity, and a flexible drive belt which is connected with the power source, passes through a wall of the cavity and then drivingly engages all of the rollers to be driven. Means, such as a waveguide beyond cut-off, is provided at the point of passage of the drive belt through the cavity wall to prevent the escape of electromagnetic energy from the cavity at such location. The belt is preferably a continuous one which frictionally engages each of the rollers directly in order to drive the same. Most desirably, the belt is also inelastic and it is the product bearing surface of the rollers which is frictionally engaged thereby. The result is that all of the rollers at the location at which they bear product will travel at the same speed.

The invention includes other features and advantages which will become apparent from the following detailed description of a preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the accompanying two sheets of drawings:

FIG. I is an overall cavity applicator incorporating the present invention;

FIG. 2 is an enlarged, partial and broken away view ofa'product support roller of the invention;

FIG. 3 is a partial side elevation of a portion of the applicator of FIG. 1 having a wall thereof broken away to illustrate the drive system in more detail; and

FIG. 4 is an enlarged, partial isometric view illustrating in more detail the manner in which the drive belt engages the rollers.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT With reference to the accompanying drawing, a multimode cavity applicator incorporating the present invention is generally referred to in FIG. 1 by the reference numeral II. Such applicator includes, as is usual, an elongated rectangular cavity 12 having dimensions relative to the frequency of the microwave energy introduced therein to support standing waves of such energy. In this connection, microwave energy sources, e.g., magnetron power packs [3, are connected via vertically upward projecting wave guides 14 (one of which is shown in detail) to flexible wave guides 16, each of which communicates through a load isolator 17 with means 18 for introducing the microwave energy into the cavity. The means 18 includes a plurality of wave guide extensions 19 which project through the top wall 21 of the cavity at spacially distributed positions into the interior of such cavity. As illustrated, each of the wave guide extensions 19 is angled within the cavity to project obliquely therein toward an interior wall of the cavity. As more thoroughly described in patent application Ser. No. 471,449 filed contemporaneously herewith and assigned to the same assignee as this application, the disclosure of which is hereby incorporated by reference, this arrangement of feed ports will result in a multitude of standing wave modes being generated and supported within the cavity and a consequent general uniform field strength throughout such cavity. The

', combination of such a feed port arrangement with the troduce such parts into the cavity, an end plate 22 at the entrance end of the cavity is provided with a pair of horizontally adjacent wave guides beyond cutoff 23 through which extruded hose parts can be fed. A corresponding pair of wave guides beyond cutoff 24 project outwardly of the cavity from an end plate 26 on the opposite or exit end of such cavity.

Immediately after being extruded, the rubber hose parts are fed through the wave guides 23 into the cavity. A product transport system, generally referred to by the reference numeral 27, is provided within the cavity for supporting the hose parts therewithin during passage through the cavity between the entrance and exit wave guides beyond cutoff 23 and 24, respectively.

Such product transport system includes a plurality of rollers 28 and a frame or mounting structure which maintains such rollers in alignment along the path of travel of the product through the cavity. As can be seen from FIGS. 1 and 3, the mounting structure includes a plurality of uprights 29 which project upward from the bottom wall 31 of the cavity to rigidly support a pair of spaced-apart and horizontally parallel support rails 32 and 33. As is illustrated, the rollers 28 extend between the rails and, as will be described in more detail hereinafter, are supported thereby for axial rotation.

As a particularly salient feature of the instant invention, the rollers 28 are not of metal as is conventional, but rather are of a combination of dielectric materials in a construction which assures that the same provide a minimum disturbance to the electromagnetic energy field adjacent product being passed through the cavity while yet being structurally sound and capable of facile rotation. As one important aspect of the rollers, the product bearing surface, i.e., that portion of the roller which directly engages a product or is most closely associated therewith during the products passage through the cavity, is defined by a cylindrical tube 34 made of quartz. Because the product bearing surface is quartz and is tubular in form, it will be transparent to electromagnetic energy within the microwave spectrum. That is, the tube will have a dielectric constant and thickness relative to such energy resulting in the same not significantly changing the direction or the magnitude of the electrical field vector of the energy upon the same encountering and passing through the tube. It has been found that the use of such quartz tubular rollers assures that the presence of the product transport system will not affect uniform heating of the product. That is, in contrast to metal rollers, that portion of a product which engages the rollers is not overheated relative to the remainder of the product. The result is that higher power levels can be used within the interior of the cavity without concern that certain portions of the product will be overheated relative to others. This is assuming, of course, that the field strength within the cavity is otherwise generally uniform. The previously mentioned feed port arrrangement for introducing the microwave energy into the cavity is instrumental in this latter regard.

As is known, quartz is not an easily worked material. It is difficult without expensive labor to precisely size and finish the same. For this reason, the mounting of the tubes 34 on bearings allowing free axial rotation thereof presents special problems. The instant invention further includes a particular combination of; roller and bearing construction which is quite simple and yet highly effective for this purpose. All of the rollers 28 and their relationship to the mounting structure is identical. FIG. 2 illustrates one in detail. As seen therein,

each of the rollers 28 includes cylindrical end plugs 36 in the opposite ends of its cylindrical tube 34. Each of the end plugs 36 is also of a dielectric material, e.g.,

polytetrafluorethylene, which will withstand the gas temperature within the cavity without losing its structural integrity, as well as being relatively transparent to I such tubes. This spacing enables differential thermal,

expansion between the tube and the end plugs to be accommodated. In this connection, a resilient cushion sleeve 37 is provided between each of the end plugs and the adjacent inner cylindrical surface of the tube. The cushion 37 will mechanically secure the end plugs to the tube in a manner accommodating differential thermal expansion. As illustrated, a pair of annular grooves 38 extend inwardly of the peripheral surface'of each of the plugs to define channels within the end plugs within which the cushion sleeve can flow to provide a good mechanical securance therebetween. A material which has been found to be especially suitable for providing the cushion sleeve is room-temperature vulcanizing silicone rubber. Such a material is a low loss dielectric material which can be inserted in a liquid form during manufacture of the rollers between the end plugs and their associated tube.

Bearing projections rigidly secured to the support rails extend inwardly therefrom axially intothe ends of the rollers 28 for rotatably mounting the same. More particularly, each of the end plugs 36 has a cylindrical cavity 39 extending axially therein. The bearing projection associated with each end of each roller includes a rod 41 which extends through a bore in its associated support rail and has nuts 42 and 43 threadably engaging the same on opposite sides of the rail to rigidly secure the projection to the support rail. As is shown, the

inward end of the rod 41 of each bearing projection is provided with a metal, spherical bearing ball 44 extend ing within the cavity 39 of its associated roller end. The metal ball 44 engages the inner cylindrical surface of the cavity. In this connection, the cavity is provided with a cup liner 46 of a hard, low friction material, such as the non-metallic glass-filled polytetrafluorethylene marketed by Flourocarbon of Anaheim, Calif. under the trademark Flourogold. The cup will provide a longlasting bearing surface for engagement by the metal bearing ball.

As is also illustrated, the ball 44 extends into the cavity to a location adjacent the end wall 47 thereof within the interior of the roller. The ball will therefore act not only as a suppoort bearing on which the roller can axially rotate, but also as a thrust bearing which will control axial movement of the roller.

It will be recognized that because the bearing ball is spherical and the bearing surface within the cavity is cylindrical, there will be a minimum of actual physical Contact between the ball and the roller. This will assure a minimum of frictional resistance to roller rotation. Moreover, the spherical-cylindrical coupling provides, in effect, a universal connection which eliminates alignment problems and the like. Also, the tolerance of the fit of the ball within the cavity need not be close since the weight of the roller will be along the upper portion of the ball irrespective of the preciseness of the ballcavity fit.

The product transport system also includes a quite simple and yet effective arrangement for axially rotating the rollers 28 from the exterior of the cavity in order to convey product therethrough. Such arrangement includes a motive power source, such as the electric motor diagramatically indicated at 51 in FIG. 3. The power source is mechanically coupled to a friction drive roller 52 which engages a continuous, closed loop flexible drive belt 53.

As is illustrated, the drive belt 53 passes through an end wall 54 of the cavity into its interior. Means are provided at the point of passage of the drive belt through the cavity wall to prevent the escape of microwave energy from the cavity at such location. More particularly, a pair of wave guides 56 beyond cutoff are provided registering with the wall apertures through which the'belt extends. The belt also extends axially through such wave guides beyond cutoff.

The belt 53 drivingly engages the rollers 28 to axially rotate the same for conveying product through the cavity. More particularly, as illustrated in FIG. 3, the upper portion of the belt passes around an idler roller 57 after entering the cavity and then extends upward where it frictionally engages the upper peripheral surface of the first roller, roller 28', along the path of travel of the product. The belt then alternately passes around idler rollers 58 and succeeding ones of the rollers 28. The belt thus frictionally engages all'of the rollers along the path of travel of the product. The belt then extends downward and passes around idler rollers 59 which guide the same on a return path for exiting the cavity through an appropriate one of the wave guides beyond cutoff 56.

It will be recognized that engagement of the drive belt directly with the peripheral surface of each of the rollers provides the driving of such rollers with a minimum of structure, e.g., no drive axles, gears, etc. More over, it is preferred that it be'the upper surface of each of the rollers which is driven as shown. especially if the product to be conveyed through the cavity has a low resistance to stretching and the like. That is, the belt 53 is inelastic, and since it engages the upper peripheral surface of each of the rollers, such peripheral surfaces will all be rotated at the same speed, irrespective of slight differences and the like in the roller diameters. It is the upper peripheral surface of the rollers which defines the support surface for the product passing through the cavity. Because all of such upper peripheral portions of the rollers will be rotated at the same speed, there will be no speed differential between adjacent rollers which might stretch or otherwise affect the shape of products being conveyed on the rollers. As stated previously, it is difficult to machine quartz to exact tolerances. This feature is therefore especially useful with quartz rollers in which there may be significant diameter differential between rollers.

As illustrated, one of the idler rollers 58 is provided between each pair of adjacent product supporting rollers 28, and the belt 53 passes around the same on the side thereof opposite to the previously mentioned product supporting portion of the product rollers. Because of this, the idler rollers act to maintain the belt in frictional engagement with a significant portion of the peripheral surface of each of the product rollers.

The simplicity and yet inherent effectiveness of the product transport system of the applicator of the invention should be apparent from the above. Although it has been described in connection with preferred embodiments, it will be recognized by those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. For example, even though it is preferred that the drive belt be a flat belt which frictionally engages the rollers directly as described, the terms belt and flexible drive belt when broadly used alone are meant to include drive chains and the like which extend into the interior of the cavity to provide driving of the rollers. It is therefore intended that the coverage afforded applicant be limited only by the language of the claims and its equivalent language.

What is claimed is:

1. An applicator for treating a product with electromagnetic energy comprising:

a cavity resonator capable of supporting electromagnetic energy within its interior;

means for introducing electromagnetic energy into said cavity; and

a product transport system within said cavity for supporting said product therein during passage thereof through said cavity for said treatment, said product transport system including a plurality of rollers and a mounting structure maintaining said rollers in an alignmment defining a support surface along the path of travel of said product through said cavity, an end of each of said rollers having a cylindrical cavity extending axially therein, and said mounting structure including a support rail extending along the path of travel of said product adjacent said ends of said rollers, and bearing projections extending inwardly of said rail for rotatably mounting each of said rollers, each of said bearing projections including a spherical bearing ball extending within the cylindrical cavity of its associated roller end and engaging the inner cylindrical surface of said cavity.

2. The applicator of claim 1 wherein each of said roller end cavities is provided with an end wall within the interior of its associated roller and the spherical bearing ball extends into said cavity to said end wall to thereby also act as a thrust bearing.

3. The applicator of claim 2 wherein each of said rollers is a cylindrical tube having an end plug in its end within which said axial cavity is provided.

4. The applicator of claim 3 wherein each of said cavities is defined by a cup liner of a hard, low friction nonmetallic material providing a bearing surface, and each of said spherical bearing balls is of a metal.

5. The applicator of claim 3 wherein the material of said end plugs has a different coefficient of thermal expansion than the material of said cylindrical tubes, and a resilient cushion sleeve is provided between each of said end plugs and its associated tube to accommodate any differential expansion between said tube and said end plug.

6. The applicator of claim 1 wherein said product transport system further includes a source of motive power positioned exteriorly of said cavity resonator, a flexible drive belt connected with said power source and passing through a wall of said cavity resonator into driving engagement within the interior of said cavity resonator with said rollers to axially rotate the same for conveying product through said cavity resonator, and means at the point of passage of said drive belt through said cavity wall for preventing escape of electromagnetic energy from said cavity thereat.

7. The applicator of claim 6 wherein said drive belt is an inelastic flat belt and frictionally engages the peripheral surface of each of said rollers at the location at which the same defines a portion of said support surface for said product to thereby drive all the support surface portions of said rollers at the same speed.

8. The applicator of claim 1 wherein said means for introducing electromagnetic energy into said cavity resonator includes a plurality of wave guide extensions projecting into the interior of said cavity resonator, each one of which projects obliquely into the interior of said cavity resonator for directing electromagnetic energy emanating therefrom angularly toward a cavity wall to generate with said energy a pluraltiy of standing wave modes within said cavity resonator.

9. The applicator of claim 1 wherein each of said plurality of rollers includes a product bearing surface which is of a dielectric material transparent to the electromagnetic radiation supported within said cavity resonator to thereby present a minimum disturbance to the electromagnetic energy field in such cavity resonator at its location, whereby the presence of said rollers in said cavity resonator adjacent product passing therethrough has a minimum effect on the uniform treatment by said electromagnetic energy of said product.

10. The applicator of claim 9 wherein each of said tubes is of quartz. 

1. An applicator for treating a product with electromagnetic energy comprising: a cavity resonator capable of supporting electromagnetic energy within its interior; means for introducing electromagnetic energy into said cavity; and a product transport system within said cavity for supporting said product therein during passage thereof through said cavity for said treatment, said product transport system including a plurality of rollers and a mounting structure maintaining said rollers in an alignment defining a support surface along the path of travel of said product through said cavity, an end of each of said rollers having a cylindrical cavity extending axially therein, and said mounting structure including a support rail extending along the path of travel of said product adjacent said ends of said rollers, and bearing projections extending inwardly of said rail for rotatably mounting each of said rollers, each of said bearing projections including a spherical bearing ball extending within the cylindrical cavity of its associated roller end and engaging the inner cylindrical surface of said cavity.
 2. The applicator of claim 1 wherein each of said roller end cavities is provided with an end wall within the interior of its associated roller and the spherical bearing ball extends into said cavity to said end wall to thereby also act as a thrust bearing.
 3. The applicator of claim 2 wherein each of said rollers is a cylindrical tube having an end plug in its end within which said axial cavity is provided.
 4. The applicator of claim 3 wherein each of said cavities is defined by a cup liner of a hard, low friction non-metallic material providing a bearing surface, and each of said spherical bearing balls is of a metal.
 5. The applicator of claim 3 wherein the material of said end plugs has a different coefficient of thermal expansion than the material of said cylindrical tubes, and a resilient cushion sleeve is provided between each of said end plugs and its associated tube to accommodate any differential expansion between said tube and said end plug.
 6. The applicator of claim 1 wherein said product transport system further includes a source of motive power positioned exteriorly of said cavity resonator, a flexible drive belt connected with said power source and passing through a wall of said cavity resonator into driving engagement within the interior of said cavity resonator with said rollers to axially rotate the same for conveying product through said cavity resonator, and means at the point of passage of said drive belt through said cavity wall for preventing escape of electromagnetic energy from said cavity thereat.
 7. The applicator of claim 6 wherein said drive belt is an inelastic flat belt and frictionally engages the peripheral surface of each of said rollers at the location at which the same defines a portion of said support surface for said product to thereby drive all the support surface portions of said rollers at the same speed.
 8. The applicator of claim 1 wherein said means for introducing electromagnetic energy into said cavity resonator includes a plurality of wave guide extensions projecting into the interior of said cavity resonator, each one of which projects obliquely into the interior of said cavity resonator for directing electromagnetic energy emanating therefrom angularly toward a cavity wall to generate with said energy a pluraltiy of standing wave modes within said cavity resonator.
 9. The applicator of claim 1 wherein each of said plurality of rollers includes a product bearing surface which is of a dielectric material transparent to the electromagnetic radiation supported within said cavity resonator to thereby present a minimum disturbance to the electromagnetic energy field in such cavity resonator at its location, whereby the presence of said rollers in said cavity resonator adjacent product passing therethrough has a minimum effect on the uniform treatment by said electromagnetic energy of said product.
 10. The applicator of claim 9 wherein each of said tubes is of quartz. 